Cylinder Head Bodge

[AlfaLofa]

Everything was looking good - a BV head which is still 4.6" deep, decent sprint cams and then.....

As I was removing the cam caps I noticed that one of the studs looked wrong.

When I released the nut the stud just disappeared through the head

So some time in the past some one had b******d up the fitting of a stud and presumably stripped the thread.

The stud hole was then extended through the head - thus enabling a bolt to be used to fit the cap

Has any one come across this type of damage before?????????????????

I assume (i.e. I'm hoping) it can be repaired properly by welding up the hole on the underside of the head, drilling an oversize hole and then fitting a helicoil or similar - any advice would be most welcome.

[rgh0]

Yes you should be able to weld it up and refit the stud with a helicoil. However you may find you need to line bore the cam tunnel again if the welding and heat distorts the bearing alignment.

cheers
Rohan

[AlfaLofa]

Hi Rohan

I've just had a thought - perhaps an alternative repair would be:

a) have the hole drilled and fitted with a helicoil
b) fill the underside of the hole with epoxy resin

Is there any reason why this wouldn't work?

This stuff is allegedly good up to 300F:

http://www.ebay.co.uk/itm/J-B-WELD-KWIK ... 3a63463245

PS
Excuse my ignorance - but out of interest, If, after welding, the cam tunnel did need line boring, how are the caps with their bearings made to fit if the tunnel is "modified" - but the stud fixing holes stay unchanged?

[Chancer]

Nice bodge!

A few years back an owner would have been singing the praises of the mechanic or helpfull guy like myself who did it, got him out of trouble and back on the road saving him loads of money compared to what the garage wanted to do the job properly.

I bet you were shocked when the stud taht wasnt a stud dropped out of sight

I favor a helicoil and a threaded insert from underneath sealed with Loctite.

[AlfaLofa]

Hi Chancer - yes I was surprised when the "stud" disappeared.

I looked down the hole and saw daylight.

And yes I'm with you - this is the sort of bodge up that I would have been proud of 40 odd years ago

I hadn't considered fitting the coil from below - nice idea.

What variety of Loctite are you advocating for sealing the bottom of the hole?

[Chancer]

Actually I hadnt thought of that but now you mention it, its a great idea!!!!

What I meant was helicoil from above and then tap a thread underneath to be sealed with either a threaded plug using a Loctite type plumbing sealer or maybe if the casting is flat a bolt and copper/fibre washer.

If the stud is located in the helicoil with a light duty thread sealer, nutlok or similar I doubt that much is any oil would find its way down through the hole.

[Hawksfield]

Hi alfalofa

I had the same problem whilst repairing a stripped stud and fitting a helicoil, I found I had drilled too deep and broke through.
I did not notice this till the job was complete and I was painting the head insitu I filled it with silicon adhesive and painted and its been that way for the last 3 years.
When the stud is fitted there is no access or egress for oil leaks and has been fine.
The next time the head is off I may relook at it but I think its best to leave as is.

[rgh0]

To line bore you would machine a small amount of the face of the caps, bolt them down and then run the line bore tool through the tunnel aiming to take the minimum amount off the head and the required amount off the caps to achieve a new straight bore. If you welded the hole up with a couple of plates bolted to the top and bottom faces of the head and were careful with the heat input you would probably not distort it ( but no guarrantees)

Repairing by tapping and plugging the hole with a screw plug or you could press fit an aluminium plug would all work and avoid the potential distortion from welding, Just really depends on how cosmetically original you want it to look, a flush press fit aluminium plug would be not really visible. The bolt bodge has worked for years so you dont really need to do anything !!!!.

cheers
Rohan

[billwill]

Hi Rohan


Excuse my ignorance - but out of interest, If, after welding, the cam tunnel did need line boring, how are the caps with their bearings made to fit if the tunnel is "modified" - but the stud fixing holes stay unchanged?

I presume that after the boring as described by Rohan, you have to use bearing shells that have a thicker steel base layer?

[rgh0]

No you line bore to the original diameter. The removal of metal off the face of the caps before boring enables this to be done as it makes the hole smaller and you bore it back to the standard diameter and only move the cam shaft centre line fractionally lower by a couple of thou in most cases.to bring all the bearings back on the same centreline

cheers
Rohan

[Ianashdown57]

You could use a blind insert and put it in with some thread-locker. There should be no possibility of a leak path.

Ian

[billwill]

No you line bore to the original diameter. The removal of metal off the face of the caps before boring enables this to be done as it makes the hole smaller and you bore it back to the standard diameter and only move the cam shaft centre line fractionally lower by a couple of thou in most cases.to bring all the bearings back on the same centreline

cheers
Rohan

Oh, I see. But won't there be a possiblilty that the new hole is slightly oval, being wider at the central horizontal plane? Assuming there was some horizontal mis-alignment before the new line boring operation.

[AlfaLofa]

Hi Bill

You are reading my mind - these are the questions I was mulling over when I asked the question about line boring.

I can't quite get my head round it.

[rgh0]

No you line bore to the original diameter. The removal of metal off the face of the caps before boring enables this to be done as it makes the hole smaller and you bore it back to the standard diameter and only move the cam shaft centre line fractionally lower by a couple of thou in most cases.to bring all the bearings back on the same centreline

cheers
Rohan

Oh, I see. But won't there be a possiblilty that the new hole is slightly oval, being wider at the central horizontal plane? Assuming there was some horizontal mis-alignment before the new line boring operation.

I agree but it works as I have seen it done on a couple of heads of mine!. The bends in the head tend to be vertical not horizontal mainly but it will pick up a small horizontal misalignment as well. The area in the head just before the join to cap is slightly out of round but this is insignificant in terms of mounting the shells it appears.

You do need to ensure the head is flat before you line bore it otherwise when its bolted down you introduce a bend again.

cheers
Rohan

[alexblack13]

I'm very glad you got there 1st this time Rohan...

Very well explained. Well done

I favor the helicoil route from the top and a slight interference fit aly plug inserted from below up to the same depth as the drillings for the st'd studs, keeping the plug a mil or two below the cleaned up surface. Then plug weld the filler 'plug' into place. It could then be machined back to give an original looking surface finish.

Remember the helicoil if properly fitted will take 1.25 x the st'd torque so will be slightly stronger.

Check the cams for free rotation with the head tightened down. Fitting the caps well lubed up and turning the cams by hand (no valves or springs of course) gently tighten down to torque whilst checking the free rotation of the cams all the time. If any of them binds or stiffens up then you will need to line bore as described in Rohan's excellent advice...

Cracking bodge by the way... 5 gold stars IMHO ...